Piezoelectric apparatus



Oct. 16, 1945. J. P. ARNDT, JR., ETAL. 2,387,108

PIEZOELECTRIC APPARATUS Filed March 18, 1942 Patented Oet. 16,v 1945UNITED .STATES PATENT ori-ICE PIEZOELECTRIC APPARATUS John P. Arndt,Jr., Euclid, and Walter J. Brown and Alfred L. W. Williams, ClevelandHeights, Ohio, assignors to The Brush Development Company, Cleveland,Ohio, a corporation ot Ohio Application March 1s, 1942, serial No.435194 (ci. 1v1-321)' Claims.

This invention relates to .piezoelectric apparatus and more particularlyto relays or the like wherein the actuating member is similar to thepiezoelectric `motor element disclosed in the lSawyer Reissue Patent20,213.

Piezoelectric crystal elements of the sodiumpotassium tartrate type havemany advantages a relay, actuated by a piezoelectric element, that shallnot depend upon critical contact spacing and one that is substantiallyunaifected by temperature changes.

Another object of the invention is to provide a relay, actuated by apiezoelectric element, that shall be rapid in action, inexpensive tomanufacture, yet extremely rugged. y

Another object of the invention is to provide a relay or tle like,actuated by a piezoelectric element, wherein alteration of the shape ofthe element, from natural causes, or at very low veloclty, does notinterfere with reliability.

istiil further object of the invention is to provide a reiay or thelike, actuated bya multipiate flexing piezoelectric element, wherein setor sag thereof shall be compensated automatically.

.In accordance with the invention, a piezoelectric element, preferably amultiplate fiexing element of the type disclosed in the Sawyer patent,is so supported in operative relation to an instru'- mentality having amovable part such, for example, as a snap-action switch, that slowchanges inthe shape of the element,` at low velocity or from naturalcauses, are continuously compensated, whereas movements thereof at .high

pivot, the free upper end being operatively connectedwith the switch.The system is in stable equilibrium and, if the resistance offered bythe switch to movement by the free end of the element is properlyadjusted. slow bending of the element is compensatedby rotary movemento! the weight about its pivot. the free end of the element beingeffectively decoupled" from the switch. When, however, potential isapplied to the electrodes of the element such as to cause it to bendwith high velocity, the inertia of the weight is such ,that it servesthe purpose of a fixed mounting, causing operation of the'switch.Another way of explaining thea'ction is by analogy to a high pass`illter, the movable part of the switch corresponding to the outputterminals thereof, and the weight corresponding to a shunt,- inginductor.

The novel features of the invention are set forth with particularity inthe appended claims. The inventionqitself, however, both as to itsorganization and its method of operation, together withl further objectsand advantages thereof, will best be understood from a consideration ofthe following description of certain specific embodiments taken inconnection withthe accompanying drawing in which:

Fig. i is a diagrammatic elevational view of one embodiment of theinvention, also showing an operating circuit therefor.

Fig. 2 is a conventionalized side elevational view of a modification ofthe device shown in Fis. 1.

velocity are transmitted to the said instrumerztality. To obtain suchaction, a piezoelectric element of either' the "bender or the "twistertype may be utilized, one portion of which is operatively engaged withthe switch at all times while another portion is permitted to moveslowly, as the element "setsj without disturbing the engage- .ment withthe, switch. Such elements are disclosed in the Sawyer Reissue Patent20,213, and

they are now well known to those skilled in `the f art. For example, abender element may be mounted' upright upon a horizontally pivotedweight, tc/flex in a yplane at right angles to the Fig. 3 is aconventionalized sectional view of an alternative embodiment of theinvention.

Fig. 4 is a conventional view,=pai'tly` in' vertical section and partlyin elevation, -of another embodiment of the invention.

Fig. 5 is a fragmentary view in perspective showing an alternativeeinbodunent oi.' the invention exemplified by Fig. 4.

Fig. 6 is a view in perspectiveoi an actual relay constructed accordingto thevinvention, part of the apparatus being broken away in order todisclose more clearly the details thereof.

In all figures of the drawing, identical elements are similarlydesignated.

Referring now to Fig. 1 of the. drawing, an' embodiment of the inventionmay comprise a weight i rotatably supported upon a horizontal pivot I onthe upper surface of which is'vertically mounted a piezoelectric crystalelement 5 of the multiplate bender type, the crystal sectionsconstituting the element being disposed in planes parallel to the planeof the weight-supporting pivot 3. The upper end of the piezoelectricelement is pi a- .nois.

vided with means such as a plurality of ilngers 1 1, or the like, whichengage the movable part t of a snap-action switch ll, or the like, ofthe type that requires only a short throw for actuation.

As is well known to those skilled in the art, snap-action switchesusually require a certain denite amount o f force to throw them from oneposition past dead center to the other position. This action may besecured by a small spring so mounted with respect to the movable part ofthe switch-or similar device that it is placed under tension as the saidmovable part moves through dead j center, the tension being relaxed ateither of the rest positions. There is also another well known short.throw switch on the market known as a micro switch, manufactured underUnited States Patent 1,960,0 by the .Micro Switch VCorporation ofFreeport, Illi- The latter switch requires a short throw for operationto the closed position, after which it tends, because of itsconstruction, toreturn to;A

the open position. A slight modification of this invention is necessaryfor the operation of a micro switch or switches of that general type,

as hereinafter will be explained in connection v with other ligures ofthe drawing.

For the purpose of causing the multiplate dexing elementi to bend toeither one side or the other, a source of potential is provided forapplication to .the inner an'd outer electrodes thereof. The source may,if desired, be unidirectional and a reversing switch (not shown) may beutilized or it may be constituted, as shown in Fig. 1, by a battery I3,a central tap I5 which is connected to the interior electrode I1 -of themultiplate flexing element, a three-point switch I9 be- Y ing soconnected to the outer electrodes 2I-2I of the multiplate flexingelement that eitherthe positive or negative terminal of the battery I3may .be connected thereto.' A bleeding resistor 23 having a resistanceusually of the order of 116 to 10 megohms is connected across theelectrodes of the multiplate flexing element for the purpose ofdissipating the charge thereon afteractuation thereof and after opening'of the switch.

The weight I is so chosen and the position of the pivot 3 is so fixedthat the system constituted bythe piezoelectric element 5 and the weightis in a state of 'stable equilibrium. Furthermore, the inertia of theweight is so related to the force required to throw-the snap-action.switch past dead center that when the crystal element 5 tends to slowlysag or set or to change its shape because of temperature changes, theswitch il is not actuated but the weight l is so moved in a small arcaround the pivot 3 as to compensate for changes in crystal lelementconguration.

.However, if potential is applied to the electrodes,

ture eiects, and to the eiects of set or sag, re-` sponding, to actuatethe switchfonly to potentials such that the crystal is caused to ilexsuddenly@ Obviously, the apparatus will be immune to very low frequencyalternating potentials if the frequency thereof is below the natural`flexing period of the crystal and weight assembly, and the apparatus,accordingly,.may be utilized to discriminate between high and lowalternating freitA , as Viscoloidf' aestgios a dierent frequency, ii thepotential is suiiip ciently high.

There are a number of modified embodiments of the invention analogous tothe device shown' in Fig. 1. For example, referring to Fig. 2 of thedrawing, the piezoelectric element 5 may be sup- -ported horizontallyupon the weight l as shown in full lines in Fig.' 2, or vertically belowthe pivot 3. In such event, the vertically suspended clement wouldfunction in exactly the same manner 'as hereinbefore described inconnection with Fig. l. A jfmicro switch" 25 may be associatedwith thehorizontally positioned piezoelectric element provided a resilientadjustment device 21 is supplied for maintaining adenite pressure uponthe free end of the element to balance the tendency 'of the movableportion 29 of the micro switch to return toits open position. The actionof the adjusting device 21 will be explained in more detail inconnection with Figs. 3 and 6 of the drawing. f'

Inasmuch as the spirit of the invention resides A in the-provision ofmeans whereby slow movement itself being relied upon to securesnapaction. Such alternative embodiment of the invention is exempliiiedby Fig. 3 of the drawing wherein one end ofA the crystal element isembedded in a mass 3| of deformable material such The free end of thecrystal element,`still referring to Fig. 3, rests upon the movableportion 29 of a snap-action switch 25, such as the micro switchpreviously referred to, and` is held against it by an adjusting device21 shown partly in section and partly in elevation. .The adjustingdevice 21 is constituted by a small plunger 33' that telescopes within ahollow screw 35 having a knurledhead 31 and is resilently urged 'againstthe upper `face of the multiplate exing element by a small spring 39interposed between the inner end ,of the hollow screw and f the top ofthe plunger. The pressure exerted by the spring upon the plunger andultimately upon Y the crystal element is determined by adjustmentA ofthe hollow screw in a yoke di such as is shown more clearlyl in Fig. 6.The pressure is made just slightly to overbalance the tendency of the Iswitch knob 29 to return to the openposition but 4it is'insulcient tocause any appreciable movement of the crystal element'such as wouldactuate the switch 25.

Il. in use, the crystal element 5 shown in Fig. 3

tends to sag or set or otherwise to'change its configuration, suchchange is permitted t a. slow rate by the semi-resilient*mounting 3i,the unscribed alternative embodiment of the invention.

A still further embodiment of the invention is exemplified by Fig. 4 ofthe drawing, wherein a snap-action switch Il is operatively connected bya rod 43, or the like, to the mid-portion of a piezoelectric crystalelement I5 of the multiplate bender type, the ends of which are fixed ina yoke 41,v which is in turn supported from the piston I9 of a. dash-pot5I. No attempt hasbeen made in the drawing to show the details of an iactual dash-pot, the essential feature of` which is the provision of avery small passageway 53 between the cylinder in which the pistoncarrying the yoke moves, and a storage reservoir 55.

, Should lthe bender type element shown in Fig. 4 tend slowly to deform,only relatively slight resistance is offered to the flow of fluidthrough the interconnecting passageway 53, and the piston moves tocompensate the changes in shape of the crystal while permitting theswitch arm 9 to remain in position. When, however, potential is appliedto the bender element, it tends to flex at l high velocity and in suchevent the passageway 53 o'ers extremely high resistance to movement ofthe fluid againstwhich the piston presses with the result that the yoke41 carrying the piezo- 'mounting means 3| shown in Fig. 3 in that afterthe crystal has slowly deformed by reason of y natural causes, norestoring force is applied to it other than the difference in levelbetween the fluid in the cylinder of the dash-pot and in the StOragechamber.

lcal planes.

As will be apparent from an inspectionof the drawing, the pairs ofcorner-clamping devices 65-61 are such as to permit a limited rockingmovement of the piezo-electric element while re-u straining any movementof the corners in verti- Accordingly, as the element sets or sags orchanges its shape because of temperature changesfno force is applied tothe switch arm, the free end of the element being permitted to moveslowly to compensate` such changes. However, when potential is appliedto the electrodes as described in connection with Fig. 1, the freecorner 68 and the corner 1| -in contact with the switch arm tend to movewith high velocity. Because of the construction of a twister typepiezoelectric element, the free corner and the corner in contact withthe switch tend to move downwardly While the clamped corners tend tomove upwardly or vice versa, depending upon the polarity of the appliedpotential. If it is assumed that the momentarily applied potential issuch as to cause the free corner to move downwardly at a high velocitywhilethe corner in contact with the switch arm also tends to movedownward, the tendency to movement of the said free corner introduces areaction into the system that is the same in kind as the reaction thatwould be introduced were the said free corner to be provided' with aweight. This effect, together with the actual inertia of the freecorner, causes the crystal to flex around an axis 'interconnecting theclamped corners with the result that the switch is moved to the closedposition where it is held by lthe resilient adjusting device until suchtime as a potential of opposite polarity is applied.

It will, accordingly. be apparent from a consideration of the foregoingdescription of several modifications of the invention, that it offersadvantages heretofore unobtainable. The invention is mainly advantageousin that it obviates all need for exact and meticulous contact spacingand in that a device constructed in accordance Referring to Fig.- 5, ifa twister element -51 is utilized in the embodiment exemplified by Fig.

4, a plurality of yokes 41 are utilized and they are connected,respectively, to pairs of opposite corners of the element.

Perhaps the simplest embodiment of the invention is one whereinresilient mountings, weights, and the like, are dispensed with and theinertia of the crystal element itself is relied upon to cause a switchto be thrown when the said element is energized. Such a device is shownin Fig. 6 of the drawing. It preferably comprises a base 59 having twouprights Si, the said uprights, respectively, serving to ,hold theopposite corners of a piezoelectric element 51 of the torque or twistertype. For clamping purposes, each upright may be provided with a slot orniche 63 having a vertically extending abutment 65 on which a corner ofthe crystal rests and against which the corner is held by a clampingscrew 61'. One corner B8 of the crystal is left perfectly free while thediagonally opposite corner 1i rests upon the upwardly extending movableoperating arm 29 of a switch 25 such as a micro switch. Thelast-mentioned corner of the crystal is resilientiy held against theoperating arm of the micro switch by an adjusting device of the typeshown in section in Fig. 3 that is mounted in a yoke 4I which extendsover the said corner. By turning the knurled head 31 of the adjustingdevice, the pressure upon the' switch arm 29 may be maintained justsuiiiclent to hold it in the closed position after actuation by thepiezoelectric element.

natural causes.

therewith is` free from the troublesome disturbance of contact spacingintroduced by setf or sag or by changes in crystal element configurationresulting from temperature changes or from other Operative engagementbetween the crystal element and the switch arm is maintained throughoutthe useful life of the device and it has proven to be very rugged andreliable in operation.

p Further advantages of the invention as well as further embodimentsthereof willlbe apparent to those skilled in the art to which itpertains. For example, any other device, capable of being actuated by arelatively small movement of an element thereof, may be substituted forthe switches shown. The invention, therefore, is not to be limitedexcept insofar as is necessitated by the prior art and by the spirit ofthe following claims.

What is claimed is:

' 1, In combination, a piezoelectric element adapted to flex rapidly inresponse to an electrical potential applied thereto, a, switch having amovable part biased into operative engagement with said element andyieldable mounting means for said element permitting it to move slowlywhile maintaining engagement with said movable part.

2. The invention set forth in claim 1, further characterized in that theswitch is of the snapaction type.

3. In combination, a piezoelectric element adapted to flex at highvelocity in response to an electrical potential applied thereto, aswitch having a movable 'part biased into operative en gagernent withsaid element, and yieldable mounting means for said element, themounting means permitting the element to move slowly While maintaining asubstantially fixed relation to said movable part.

t. The invention set forth in claim 3, further characterized in that theswitch is of the snap-1V action type.

5. in cornbii'iation, a piezoelectric element, a switch having a movablepart operatively associated with said element for actuation thereby athigh velocity and a yieldable support for the element against which itreacts during actuation o the movable part, said support permitting theelement to move slowly While nriaintaining operative association withthe movable part.

6. The invention set forth in claimt, further characterized in that theswitch is of the snapaction type.

7., In combination, a. piezoelectric element, an instrumentality of thesnap-action type having a movable part in operative engagement with aportion oi the element, and a support for the element againstwhich itreacts during operation of the instrumentality, the support oiering alargel opposing force to movements of the crystal at high velocity andrelativeif/- small opposing force to movements thereof at low velocity,whereby only movement at high velocity is imparted to the said movablepart.

8. in combination, a piezoelectric element, a carrier therefor includinga weight, means supporting the weight for rotary movement around anv amsadiacent to its center of gravity, the entire movable system being soconstructed and arranged that it vis in stable equilibrium.

d. 1in combination a piezoelectric element, an instrumentality oi' thesnap-action type having a movable member, means 'for establishing andmaintaining operative engagement between said movablemember and oneportion of the piezo-v electric element, and mounting means for holdinganother portion of said element in semi-fixed position, the saidmounting means substantially impeding rapid motions of the portion ofthe element supported thereby while permitting slow movements thereof.

lo. The invention set forth in claim 9, further characterized in thatthe said mounting means incl'udes la. material having high internalviscosity,

1l.` The invention set forth in claim 9, further characterized in thatthe of the multiplate flexing t i2. In combination, a piezoeltricelement and a carrier therefor constituted at least in part by adash-pot.

piezoelectric elementis/ acentos i3. in combination, a piezoelectricelementand a carrier therefor comprising a dash-pot and means connectingthe element to the dash=pot.

1i. In combination, a piezoelectric element, means of the snap-actiontype having a movable part inoperative engagement with a movable portionof the element, said movable part exerting a first'orce against themovement of the element which upon said torce being overcome actuatessaid snap-action means, means associated with said element for exertinga second force against movement of said element, said force er.. ertedby said associated means due to set or sag or" said piezoelectricelement being insuiiicient to overcome said rst force and causeactuation oi said snap-action means, and said force exerted by saidassociated means due to operation of said piezoelectric element beingsufcient to overcome said iirst force and cause actuation of saidsnapaction means.

15. The invention as set forth in claim l, rar ther characterizedbymeans for adjusting the force of the bias.

` 16. In combination, a piezoelectric element adapted to flex rapidly inresnonseto an electrical potential applied thereto, a switch having amovable part biased into operative engagement with. said piezoelectricelement, and movable mounting means for said piezoelectric elementpermitting said element to move slowly while maintaining engagement withthe said movable part of said switch without actuating said switch, theresistance of said mounting means-to move ment when said element le'xesrapidly causing said switch to be actuated.

l7. The invention as set forth in claim i6, further characterized inthis: that said movable mounting means comprises a mass of deformablematerial vvithin which a portion of said piezoelectric element isembedded.

18. The invention as set forth in claim lo, further characterized inthis: that said movable mounting means comprises pivotably mountedinertia means to which a portion of said piezoelectric element isconnected.

19. nThe invention as set forthin claim 5, further characterized inthis: that said yieldable support comprises deformable material withinwhich a portion of said piezoelectric element is embedded.

20. The invention as set forth in claim 5, iurther characterized inthis: that said yieldable' support comprises pivotably mounted inertiameans to which a portion of said piezoelectric element is connected.

- JOHN P. ARNDT, Jn.

WALTER J. BROWN. ALFR L. W. wl

